Antimatter in the Universe and the PAMELA/FERMI/AMS… anomaly Gerry Skinner...

Antimatter in the Universe and the PAMELA/FERMI/AMS… anomaly

Gerry [email protected]

Max-Planck Institut fur Extraterrestriche Physik , Garching

Max-Planck Institut fur Astrophysik , Garching

(Honorary) University of Birmingham, UK

(Department of Astrophysics and Space Research)

(Ex) University of Maryland

(attached to NASA Goddard Space Flight Center)

(Ex) Université Paul Sabatier, Toulouse

(attached to Centre d’Etudes Spatiales des Rayonnements)

mailto:[email protected]

There is direct evidence for 1) Anti-protons and positrons ~0.1-100 GeV in Cosmic Rays

2) The annihilation of 1043 low energy (<~ keV) positrons per second in the Inter-Stellar Medium

Electron Positron Annihilation

e-

g

g

e+

e+

e-

ortho-positronium3/4

para-positronium1/4

e+

e-

g

g g

g

g

• Direct annihilation

• Annihilation via positronium (Ps) formation

Positronium continuumE < 511 keV

Annihilation lineE = 511 keV

t = 1.2×10-10 s

t = 1.4×10-7 s

Leventhal, MacCallum & Stang Ap J 225 L11 (1978)

Line flux (12.2 ± 2.2) × 10-4 cm-2 s-1

in 15° FWHM field of viewCentroid (510.7 ± 0.5) keV

Integral has confirmed earlier conclusions that the positronium fraction is close to unity.

fp = 94 ± 6% (Sazonov et al, 2005)

fp = 97 ± 2% (Jean et al., 2006)

fp = 100 ± 2% (Churazov et al., 2011)

Cold H2

Hot

Warm, Ionized

WarmNeutral

Cold H

Line shapes expected for annihilation in different media

Gessoum, Jean, Gillard (2005)

The detailed 511 keV line shape observed by INTEGRAL-SPI implies annihilation is in a mixture of warm neutral and warm ionized environments

Jean, et al. (2005)

Distance traveled before annihilation as a function of initial positron energy according to the analysis of Jean et al (2009) . Upper and lower extents of a band are shown for each medium. Data are for travel along field lines. The corresponding plot for transverse motion is similar with somewhat lower values.

Higdon et al.

Boehm et al.

Centre ofthe Galaxy

NearestStar tosolar system

Earth-Sun

40° 0° 40°

Example of a model found by simulated annealing that fits the data

180° 0°90° -90° -180°Galactic longitude

0°90° -90° -180°180° Galactic longitude

40° 0° 40°

Example of another model found by simulated annealing that fits the data equally well

The problem is not that we don’t know how the positrons could be produced …

… it is that there are too many possible explanations !

Hypernovae/GRB explosions in the galaxy (Lingenfelter &Heuter, 1984; Bertone et al., 2006)

Galactic Supernovae (Ramaty & Lingenfelter, 1979 )

Galactic Supernovae + escape from the disk (Higden et al., 2007)

Novae (Clayton & Hoyle, 1974; Jose, Coc & Hernanz, 2003)

LMXBs (Prantzos, 2004)

HMXBs / Micro-Quasars (Guessoum et al, 2006)

Wolf-Rayet stars (Dearbourne & Blake, 1985)

Red Giants (Norgaard, 1980)

Pulsars ( Sturrock, 1971)

Millisecond pulsars (Wang, 2005; 2006)

Cosmic Ray interactions with matter (Ramaty, 1970)

Light (MeV) dark matter (Boehm et al., 2004)

‘Heavy’ 500 GeV dark matter + de-excitation from an excited state (Finkbeiner & Weiner, 2007).

Sgr A* (Titarchuk & Chardonnet, 2006; Totani, 2007; Alexis et al, 2013)

Color superconducting dark matter droplets (strangelets) (Oaknin & Zhitnitsky, 2005)

"INTEGRAL's journey through the high energy sky” Rome, Oct 15-18 2013

Intergalactic space (Vecchio et al., 2013)

Small H atoms (Va’vra, 2013)

Dichromic dark matter (Bai et al., 2013)

Ratecentury-1

Production M ⊙ per event

Escape probability

Positrons × 1043 s-1

44Ti 0.4/2.1SNIa/SNII

2×10-5 /2×10-4 100% 0.17-0.51

56Co 0.4/2.1SNIa/SNII

0.6/0.1 1.5-15% 0.31-3.1

26Al Rate from 1809 keV line non issue 0.20-0.33

22Na ~1000[ ONe novae)

2×10-8 100% 0.01

Total 0.69-3.95

To explain

2.6-3.4

Data from :Martin et al. (2012)Higdon et al. (2009)Hernanz (2005)Prantzos (2011)

Positrons from radioactive decay

1809 keV 26Al

Another processes that certainly produces positrons:

Cosmic Ray interactions with the ISM

(99%)

(1%)

(99.99%)

(100%)

X = other products (includes anti-protons)

€

pp →π + X

pp →K + X

K ± →μ ±ν μ

K ± →π 0π ±

π 0 →γ γ

π 0 →γ e−e+

π + →μ +ν μ

μ + →ν μν e e+

Masses

K± 493.7 MeV/c2

K0 497.6

π± 139.6

π0 135.0

m 105.7

Positrons produced have energies

10 MeV GeV➞Energy distribution of positrons from p+/m+ decay

(Stecker, 1969)

Gamma-ray excess due to annihilation in flight of high energy positrons

The curious fact : - there isn’t any excess

Conclusion :

The positrons cannot have originated at energies greater than a few MeV

Cosmic ray positrons cannot explain the observed 511 flux (anyway, there are not enough of them and they are produced mainly in the disk)

Sizun et al., (2006)

100 MeV

3 MeV

MeV excess from annihilation in flight

Need a separate component to explain the ‘bulge’ emission which is more concentrated than almost all of the proposed positron sources.

Transport should only allow the positrons to diffuse away from their origin, and so make the emission more diffuse, so must be very compact. Some possibilities :-

• Mini-Quasar-like outburst from the GC black hole 105-106 years ago

• Burst of star formation ditto

• Dark matter annihilation – arguably must be low mass (~MeV)

• Decay of excited dark matter – must be a 2-body (r2) process

IC 443 Supernova remnant

Age 10, 000 years ∼

Distance 1.5 kpc

67.5 MeV

Ackermann et al., (2013)

Gamma-rays from p0 decay

Also

W44 Supernova remnant

Age 10, 000 years ∼

Distance 2.9 kpc

• More direct evidence – Cosmic Rays measured inside the Solar System

Model and low energy observations (Mosalenko et al (2002)

Golden et al (1996)

Anti-protons and positrons are seen in Cosmic Rays

Early balloon measurements of positron fraction hinted at an unexpected excess at high energies

Posi

tron

frac

tion

→

PAMELA Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics Launched June 2006

PAMELA – pre-launch prediction

Posi

tron

frac

tion

➞

)

Adriani et al (2009)

Positron excess seen with PAMELA

Posi

tron

frac

tion

➞

Ackermann et al. (2012)

Further confirmation with Fermi using the Earth’s magnetic field

AMS-01 1998 prototype flown on Shuttle; Data link problems – little dataAMS-02 ~1999 Too much power for a satellite; moved to Space Station

2003 Columbia disaster – no room for launch in revised manifest2008 Special bill passed by Congress and Senate and signed by

Obama to add an extra Shuttle mission to allow AMS-02 to be installed

on ISS2009 Problems with superconducting magnet

– replaced with permanent one from AMS-012011 Launch

AMS-02 on Space Station

Adriani et al (2013)

AMS-02 data

Pamela data

Positron excess confirmed with AMS-02

Ground-based experiments cannot distinguish positrons from electrons but confirm an excess in the total

Borla Tridon et al (2011)

M.A.G.I.CHESS

Aharonian et al. (2009)

Proposed explanations of the ‘Pamela Excess’

1) Nearby Pulsars

Rotating B field -> ➞ E fieldDV~ 1016 VCurvature Radn ➞ g + g B e➞ ++e-

+ g g e➞ +

2) Dark Matter annihilation or decay

560 out of 1164 citations of the Adriani et al (2009) Nature paper on the Pamela excess contain ‘dark’ in the title; 761/1164 mention it in the abstract.

Malyshev, Cholis & Gelfand (2009)

Anti Stars; Anti Galaxies; Anti Clusters ?

Dirac in his 1933 Nobel Lecture :

“….One might perhaps think that the same theory could be applied to protons. This would require

the possibility of existence of negatively charged protons forming a mirror image of the usual

positively charged ones. .

… we must regard it rather as an accident that the Earth (and presumably the whole solar system),

contains a preponderance of negative electrons and positive protons.

It is quite possible that for some of the stars it is the other way about, these stars being built up

mainly of positrons and negative protons. In fact, there may be half the stars of each kind. The two

kinds of stars would both show exactly the same spectra, and there would be no way of

distinguishing them by present astronomical methods”.

Anti-deuterons – a very small population of secondaries is expected from CR interactions

Consistent with upper limits

A certain detection of even one anti-Helium nucleus in CR would be decisive.

AMS-01 set tight limits NHe/Nhe < 10-6

AMS-02 results that are awaited They should be 1000x more sensitive.

Anti Stars ?No – at least not in equal numbersWinds from starsSuperNova explosions return (anti)matter to the InterStellar MediumLimits < 1 in 104

Anti Galaxies ?No – at least not in equal numbersX-ray observations show that there is an InterGalactic medium in clusters that has been processed through stars No gamma-rays seen

Anti Clusters ?Difficult to excludeIn one case two colliding clusterscannot have been one matter,one antimatter

In principle, one CAN detect matter / anti-matter mixtureswith electromagnetic radiation

PulsarPolarizedsource

Rotation measure Dispersion measuret l3l2q

Gravitational redshift

The gravitational potential of the galaxy is well established from the velocity profile (which shows it to be dominated by dark matter)

For radiation coming from 1 kpc from the centre (an angular offset of 7°), there will be a redshift of 1 part in 106.

Would negative gravitation mass for positrons mean that 511 keV positronium annihilation radiation would show no such redshift ?

But1) The effect is small to measure at present2) The redshift is a GR effect, but GR cannot

hold

The END

Predicted e+ + e- flux from a pulsar at a distance of 1 kpc with hW0=1049 erg, an injection index n=1.6, and an injection cutoff 10 TeV



Pulsar Age (y) Distance (kpc)

Geminga J0633+1746 3.7×105 0.25

Monogem B0656 +14 1.1×105 0.28

e.g. Yin et al. (2013)

from Sahu (2012)


By assuming a distribution of pulsars, or equally by considering dark matter with clumps (`sub-halos’) at different distances, one can even explain the features in the total lepton spectrum that may (or may not) have been seen with the ATIC balloon payloads.

Panov (2013)

e+ + H → Ps + pthreshold 6.8 eV

e+ + He → Ps + He+

threshold 17.8 eV

MeV (plus)

e+

Charge exchange

Annihilationwith bound

e- in H, He..

Annihilation

with free e-

Radiativere-

combination

Collision with grains

3Ps 1Ps

In flight

Pick -off

Based onGuessoum, et al., (1991)Murphy, Share & Skibo, (2005)

3g 2g 2g2g 2g

Break -up

3/4 1/4

Thermalisation

High fp excludes many processes from being the dominant one

× ×××

×

Positron Emission Tomography (‘PET scan’)

Detector 2

Detector 1

n

-+

~ 1 m

~ 1 m

~ 1 mm


• One knows, with limited precision, on what line the annihilation took place, but not where along it.

• Knowledge of where the positron was produced is limited by its stopping distance

Positron Emission Astronomy

Gamma-ray Telescope

n

-+

~ 8 kpc

~ 100pc

?Detector 2

Detector 1

n

-+

~ 1 m

~ 1 m

~ 1 mm

Positron Emission Tomography (‘PET scan’)

Prantzos, et al. (2011)

106 yr10

3 yr

1 yr

t = E/(dE/dt)

But these are distances along the path

Gyro radius is small

Pitch angle scattering

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

. . . . . . .

After scattering, particle spirals around a different, but nearby and nearly parallel, field line. But the pitch of the spiral, and hence speed along the line, may be different – even reversed

Diffusion-like process with a random walk along (in tight spiral around) field lines

€

10−10 B

5 μG

⎛

⎝ ⎜

⎞

⎠ ⎟ γ 2 −1 pc

€

F ∝ (ρ DM )nFitting a model with a disk from radio-active decay plus a bulge component with and based on an NFW dark matter profile

€

ρDM

(* 1.2×106 dof)

*


“We show that the position of the central dark matter (DM) density peak

may be expected to differ from the dynamical center of the Galaxy by

several hundred parsecs.”

Invoked to explain an offset in the centroid of the possible Fermi 130 GeV line by ~1.5° from the Galactic centre (to negative galactic longitudes).

Antimatter in the Universe and the PAMELA/FERMI/AMS… anomaly Gerry Skinner...

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